Both in continuously variable and in infinitely variable automatic transmission, it is normal to adjust a certain gear or a certain ratio of a transmission control depending on an accelerator pedal signal which is fed to the electronic transmission control. In case of infinitely variable automatic transmissions, any ratio can be adjusted within a preset ratio range. This can result in any change of the accelerator pedal signals, however small, leads to a change of the adjusted ratio. Driving situations exist in which this leads to undesired ratio adjustments and thus to undesired rotational speed curves of the prime mover. A situation in which such an undesired rotational speed variation often occurs is the following.
In a drive at constant velocity, a driver continues to depress the accelerator pedal in order to accelerate. At the end of this accelerator pedal movement, the driver often goes light on the gas, that is, he moves again the accelerator pedal in the other direction so that a corresponding change of the accelerator pedal signal is also produced. The consequence of this is that the rotational speed curve of the prime mover has an overshoot not plausible for the driver since the gas release occurs involuntarily. Such an effect does not occur in continuously variable automatic transmission since the gear is always the same within a certain range of the accelerator pedal signal, that is, the same transmission ratio.
Control methods for continuously variable automatic transmission are known in which only discrete ratio steps are inserted so as to simulate the behavior of a continuously variable automatic transmission. Allowance must, of course, be made for the disadvantage that the prime mover—the same as in multi-speed automatic transmissions—often is not operated in the optimal operating range.
The problem on which the invention is based is to outline a method for adjusting a ratio of a continuously variable automatic transmission in which the above mentioned undesired rotational speed change of the prime mover does not occur without allowance having to be made for the disadvantages of a system which simulates the behavior of a multi-speed automatic transmission.